如何解決javascript截取字串中文亂碼問題

function subString(str, len, hasDot)  //js截取中英文字符串无乱码
        {
            var newLength = 0;
            var newStr = "";
            var chineseRegex = /[^\x00-\xff]/g;
            var singleChar = "";
            var strLength = str.replace(chineseRegex,"**").length;
            for(var i = 0;i < strLength;i++){
                singleChar = str.charAt(i).toString();
                if(singleChar.match(chineseRegex) != null){
                    newLength += 2;
                }else{
                    newLength++;
                }
                if(newLength > len){
                    break;
                }
                newStr += singleChar;
            }
             
            if(hasDot && strLength > len){
                newStr += "...";
            }
            return newStr;
        }
         
        //var subdescription = subString("js截取中英文字符串无乱码",10,true)
        //document.write(subdescription);